U.S. Pat. No. 6,581,480 B1 discloses a torque sensor arrangement comprising a shaft appropriately mounted to have a torque applied at one end portion thereof acting to rotate the shaft upon a longitudinal axis, the shaft having a transducer element comprising an internal portion of the shaft that is magnetized to emanate an external magnetic flux that is a function of a torque applied about that longitudinal axis, the transducer element having axially-spaced end portions defining magnetic pulse of opposite polarity between which the external flux is emanated to have an essentially axial-directed component a location intermediate the end portions, a sensor arrangement comprising first and second sensors located adjacent to the transducer element intermediate the end portion thereof and responsive to the axial-directed component of the magnetic flux emanated thereby, the first and second sensors being disposed adjacent radially opposite sides of the elongated member with respect to the longitudinal axis and signal processing means to which the first and second sensors are connected in an additive manner to develop an output signal representing the torque about the longitudinal axis.
WO 02/063262 A1 discloses a longitudinally magnetized transducer element. A region of a shaft may be given a permanent or stored longitudinal magnetization by locating it within a helical coil and rotating the shaft about its axis. When applying a pulse of direct current to the helical coil to magnetize at least an annular zone of the shaft. Successive pulses of opposite polarity are preferably employed, the first of higher magnitude saturating the shaft to greater depths, the second of lower magnitude to saturate the shaft to lesser depths. This provides outer and inner annuli of opposite polarity magnetization. The coil may be energized with alternating current while the shaft is moved axially through it in a pre-magnetization procedure to magnetically cleans or de-gauss the shaft. The coil may be energized subsequent to magnetization with alternating current at a lower magnitude and/or higher frequency than for pre-magnetization without the post-magnetization fields destroying the desired pattern of magnetization.
WO 99/56099 discloses a magnetizing arrangement for torque/force sensors. A magnet or elastic transducer for sensing a torque in a shaft is formed by circumferentially magnetizing a magnetisable integral portion of the shaft. To assist in the emanation of a flux dependent torque, the transducer element portion of the shaft may have further circumferentially magnetized portions to each side. These further portions are of opposite polarity magnetization to that of the transducer element. The external magnetic flux emanated by the transducer is a function of torque and is detectable by a magnetic field sensor. An alternative means for the same purpose is to provide the transducer element at a portion of the shaft having an integral annular section of raised profile projecting beyond the adjoining portions of the shaft. The shaft may be provided with a series of circumferentially magnetized portions of alternating polarity. A shaft having the whole or an integral portion of it magnetized, it can also be used to provide a force transducer sensitive to bending moment induced in the shaft by a force to be measured.